1. Field of the Invention
The present invention generally relates to high efficiency vehicle headlamps employing arc discharge light sources and, more particularly, to an arc discharge headlamp in which a single arc discharge light source generates both a high beam and a low beam pattern.
2. Description of the Prior Art
Arc discharge light sources are desired to be used in vehicle headlamps. These sources have high efficiency and high brightness, which allow the height and overall size of the headlamp housings to be reduced and, therefore, have been popular for use in current vehicle headlamp styles which for vehicular design considerations require a relatively small, thin headlamp. Generally, prior art arc light source vehicle headlamps require one arc light source and housing for the low beam and one arc light source and housing for the high beam. This significantly increases the cost of the system. In addition, when the arc light source for high beam operation is initially ignited, condensed mercury momentarily drops the brightness of the beam to approximately 15% of its ultimate value. While the effect lasts less than a second, it can be objectionable when switching on the high beam lamp.